Light-image forming materials which can be used in the field of proof paper, printing out paper, overlay films, etc., have been conventionally applied to many photographic fields as free radical photographic materials whose sensitive areas are visualized by image exposure.
Methods in which various leuco dyes are developed to the corresponding colored dyes by radical oxidation by using photo-oxidizing agents, are particularly effective for these uses. However, these dyes are sensitive to light so that even after a dye image is formed by exposure, color is also generally formed, upon exposure to
To retain an image after once the image is formed, unirradiated areas during exposure must be kept undeveloped. For example, it is known to preserve an original image by applying a solution of a reducing agent such as a free radical trapping substance to a material having an image formed thereon, for example, by spraying said solution on said material or impregnating said material with said solution. However, there is a serious problem caused by this wet process in that its working and operation become complicated. In the specification of JP-A-47 12879 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), there has been proposed a process in which an image is formed by ultraviolet light and fixing is carried out by activating a photo-reducible substance with visible light. However, this process has problems in that an apparatus must be exclusively used during the operation, because light must be used twice, and in that a spectral filter must be replaced with another one, because two different lights must be used. In the specification of JP-B-43-29407 (the term "JP-B" as used herein means an "examined Japanese patent publication"), there has been proposed a process in which heat fixing is carried out after the image exposure either by incorporating a reducing heat fixing agent in a light-sensitive layer, or by coating the surface of the light-sensitive layer with the heat fixing agent. However, this process has a problem in that lowering in sensitivity is caused with the passage of time, because light-sensitive components (leuco dye and photo-oxidizing agent) exist in close vicinity to the fixing agent Further, since the above-mentioned light-image forming material is coated on the surface of a support by using organic solvents, the manufacturing plant thereof must be provided with an explosion-proof provision. Therefore, this process has disadvantages in safety and cost.
In order to solve these problems, there has been proposed a light image forming material in which the leuco dye and the photo-oxidizing agent are enclosed in microcapsules and the reducing agent is allowed to exist outside the microcapsules (Japanese Patent Application No. 62-259111 (corresponding to U.S. Pat. application Ser. No. 07/257,580 filed on Oct. 14, 1988)). However, such light-image forming materials have such problems that image-reproducibility, fresh storage property and image-preservability are still insufficient, heat fixing rollers are stained during heat fixing and background parts after heat fixing turn yellow with the passage of time.